A basic process for the production of particulate arylene sulfide polymers from polyhalo-substituted aromatic compounds, wherein the halogen atoms attached to ring carbons react with a sulfur source while in the presence of an organic amide at an elevated temperature, is generally known in the art. Due to a continually growing attractiveness toward thermoplastic polymers, a great amount of work has been completed which has resulted in the disclosure of methods for both batch and continuous operations to produce particulate arylene sulfide polymers from polyhaloaromatic compounds having at least two halogens constituents per molecule.
One problem often associated with arylene sulfide polymers is their tendency to discolor when subjected to certain conditions. Specifically, arylene sulfide polymers which have not been subjected to elevated temperatures (i.e., at least about 100.degree. C.), and/or which are not in the presence of materials which are capable of imparting color to the polymers, are generally substantially white in color. However, during high temperature recovery, treatment and/or processing procedures, these arylene sulfide polymers often undergo considerable darkening.
Most of the polymerization processes for producing particulate arylene sulfide polymers result in the polymer being present in a reaction mixture slurry, wherein the solid component thereof comprises a mixture of a particulate arylene sulfide polymer and particulate salt by-product materials, and wherein the liquid component thereof comprises a mixture of water, an organic amide, unreacted monomer and other liquid by-product materials. In order for the resulting arylene sulfide polymer to be useful in commercial applications, it must first be separated from the undesired solid and liquid components from the reaction mixture slurry.
Upon recovering the arylene sulfide polymer from the reaction mixture slurry, traces of the particulate salt by-product, the organic amide, the unreacted monomer, water and the other liquid by-product materials are generally recovered therewith. The concentration of these trace impurities present in or on the recovered arylene sulfide polymer reduce the purity and, thus, the quality of the polymer.
The amount of impurities present in or on the particulate arylene sulfide polymer can be determined by a number of techniques known by those skilled in the art. A common method often employed is burning the particulate arylene sulfide polymer until only ashes remain. The amount of ashes which remain are indicative of the amount of impurities in or on the polymer. Since it is commercially desirable to reduce the degree of impurities in or on a particulate arylene sulfide polymer, this can be viewed as a desirability to reduce the ash content of a burned polymer sample.
One method of separating the particulate arylene sulfide polymer from the undesired impurities therein and/or thereon is generally accomplished through a number of high temperature washing procedures. Each such washing procedure is generally performed in a closed vessel and comprises slurrying the particulate polymer recovered from the polymerization reaction mixture slurry with a liquid medium (e.g., water). The slurry is agitated while the temperature and pressure within the closed vessel is elevated (e.g., at least about 100.degree. C. (212.degree. F.) but below the melting point of the polymer and at least about 100 psig). This heated slurry is then cooled; and, thereafter, the washed particulate arylene sulfide polymer separated therefrom.
Although such washing procedures do result in removing a substantial amount of solid and liquid impurities from the particulate polymer recovered from a reaction mixture slurry, there are, however, disadvantages associated therewith. The most prominent disadvantage is that the resulting particulate arylene sulfide polymer is often discolored when compared to the color of the polymer prior to the high temperature washing process. Specifically, as stated earlier, particulate arylene sulfide polymers, as recovered from a polymerization reaction mixture slurry, are generally substantially white in color. However, after such a high temperature water-wash procedure, as described above, the color of the resulting polymers generally ranges from tan to dark brown.
In many commercial applications, it is highly desirable to separate the particulate arylene sulfide polymer from the undesired solid and liquid materials contained in the reaction mixture slurry. However, equally as desirable is to prepare and/or employ, in downstream processing, particulate arylene sulfide polymers which are substantially white in color and/or have not been subjected to a significant degree of discoloration. Therefore, one object of this invention is to provide a process which results in a recovered particulate arylene sulfide polymer of reduced impurity concentration and reduced degree of discoloration.
Other aspects, concepts and objects of this invention will become apparent from the following Detailed Description when considered with the appended claims.